Lynne Spears tells how Jamie Lynn revealed pregnancy

NEW YORK -- The mother of Britney and Jamie Lynn Spears said Jamie Lynn told her she was pregnant in a note.

Lynne Spears said on NBC's "Today" show Wednesday that Jamie Lynn -- 16 years old at the time -- handed her the note and told her to go into the bedroom and read it.

The note said she was pregnant but "everything was gonna be OK, mom" and that she and boyfriend Casey Aldridge were going to raise the baby.

"I thought it was a joke," Spears said in an interview. "I kept waiting for the punch line."

Spears said she realized it wasn't a joke because Aldridge, a pipe-layer from Liberty, Miss., wouldn't look at her.

"I was just truly in shock and then I started to cry. And then she started consoling me at that point," said Spears, who writes of Jamie Lynn and her older daughter, Britney, in her new memoir, "Through the Storm."

Lynne Spears said she blames herself for what happened.

"As a mother, don't we always blame ourselves? I mean, we're the first one that's gonna take the blame," she said. "We never get the credit, but we always question ourselves and say, 'What did I do? We had this talk just a month ago.' I mean, I had no idea. I took a lot of the blame. I took all the blame."

Jamie Lynn and Aldridge welcomed daughter Maddie Briann in June.

The couple are now engaged.